Note 25 at Mt 23:35: Abel was the first righteous martyr mentioned in the Scriptures (Ge 4:8), and apparently the prophet Zechariah was the last. Zec 1:1 makes it very clear that the prophet who wrote the Old Testament book bearing his name was the same "son of Barachias" that Jesus was speaking of here. Therefore, Jesus added to the knowledge of this Old Testament saint by revealing that he was martyred between the temple and the altar. It is unclear if this is the same Zechariah, the son of Jehoiada, who was killed in 2Ch 24:20-21.

By Jesus referring to the first and last martyrs listed in Scripture, He was saying that all of the blood of righteous people of all times would be required of this generation. This was appropriate, since the blood of Jesus, whom they would slay, would be worth infinitely more than all of the other martyrs' blood combined.